NEURAL MECHANISM FOR BILATERAL INTEGRATION IN SOMATOSENSORY CORTEX

Sensory perception requires processing of stimuli from both sides of the body. Yet, how neurons bind stimulus information across the hemispheres to create a unified percept remains unknown. We performed large-scale recordings from neurons in both somatosensory cortices (S1) in mice performing a task requiring active whisker touch to coordinate stimulus features across hemispheres. When mice touched reward-associated stimuli, their whiskers moved with greater bilateral symmetry, and synchronous spiking and enhanced spike–field coupling emerged between the hemispheres. This coordinated activity was absent in stimulus-matched naïve animals, indicating that interhemispheric coupling involves a goal-directed, internal process. In S1 neurons, addition of ipsilateral touch primarily facilitated the contralateral principal whisker response. This facilitation primarily emerged for reward-associated stimuli and was lost on trials where mice failed to respond. Silencing of callosal S1 signaling reduced bilateral facilitation and interhemispheric synchrony. These results reveal a state-dependent logic that augments the flow of tactile information through the corpus callosum.

Building on this framework, we further investigated how goal-directed behavior shapes temporal encoding of self-motion within S1. We found that approximately half of the S1 population encoded whisker self-motion during free-air whisking, with similar tuning properties in expert and naïve animals. During contralateral principal whisker touch, expert mice exhibited significantly sharper phase tuning, with preferred phase angles tightly clustered near protraction and greater modulation depth compared to naïve mice. Ipsilateral whisker touch alone did not evoke additional spiking responses in most S1 neurons, but in expert animals, it enhanced phase-specific firing without increasing overall spike rates. These results suggest that goal-directed training enhances temporal features of self-motion encoding and facilitates interhemispheric integration through refined, phase-locked activity in S1 neurons.